The present invention relates to a device for and a method of detecting a relative movement between two machine parts which are movable relative to one another, wherein one of the machine parts has a plurality of marking rulers arranged one after the other in direction of the relative movement of the machine parts.
Patent documents DE-OS 1 773 460 and DE 196 21 015 A1 show a methods and devices, in which a plurality of marking rulers are utilized and arranged on one of the machine parts one after the other in direction of a relative movement of the machine parts. Two sensors are provided on the respectively other machine part for sensing the marking rulers. The marking rulers carry increment markings arranged at uniform distances and sensed by the sensors. Thereby the location resolution obtainable during the detection of the relative movement of the machine parts is provided by the predetermined distance of the increment markings. The transition from a first marking ruler to a second marking ruler is detected by a comparison of the sensing signals of the both sensors. In order to guarantee an orderly detection from one marking ruler to a next marking ruler, both marking rulers must be joined with one another with an accuracy which does not exceed the resolution of the marking rulers, or in other words a predetermined distance of the increment markings.
The prospectus of Rexroth Star GmbH “STAR-Kugel-und Rollenschienenführungen mit integriertem Messsystem” discloses devices with a single marking ruler, in which an evaluating unit, based on the phase length of the sensing signal of the sensor, determines the absolute position of the corresponding sensor between two successive increment markings. With a distance of the increment markings in the order of 1 mm, a resolution of less than 1 m can be obtained.
In order to complete the evaluation, it should be mentioned also the documents DE-OS 2 4 16 212 and EP 0 350 158 A1. In the devices disclosed in these references, the marking rulers have additional reference markings which allow the detection of the absolute position of one machine part relative to the other machine part.